Reverse PTR

I have noticed that ISPConfig 3.0.1.6 supports PTR records. Does it mean that it is possible to create reverse PTR record into DNS zone, so you don't have to rely on your ISP? If "Yes" that params I should fill in for PTR records?

So in my current case the place I rent the rackspace from for my server. In their control panel I can set reverse dns name. I have that set to the name of my server: grumpy.system6hosting.com. But I'm still getting some emails rejected from some places (like craigslist) saying my dns does not match my rdns. Not sure what to do.

Yes what? I have 10 IP addresses. 2 are set to ns1.system6hosting.com and ns2.system6hosting.com. The other 8 have grumpy.system6hosting.com. What do I ask them to do? Set a PTR record to what? Sorry if I'm easily confused.

EDIT: It appears to be the place (craigslist.org) sending the rdns/dns errors doesn't accept emails from any domain with the word 'host' in it. So my system6hosting.com domain is getting rejected and sending the misleading error. Other domains on my same server go thru without problems. PITA.